High-pressure vapour lamp containing indium, thallium and gallium halides



P. DELRIEU ETAL AND GALLIUM HALIDES Filed OCT.. 11, 1965 HIGH-PRESSURE VAPOUR LAMP CONTAINING INDIUM, THALLIUM April 23, 1968 United States Patent O 3,379,916 HIGH-PRESSURE VAPUR LAMP CNTAIN- ING INDIUM, THALLIUM AND GALLIUM HALIDES Pierre Delrieu, Paris, and Andr Taxil, Rueil-Malmaison, France, assignors to Claude Paz et Visseaux Filed Oct. 11, 1965, Ser. No. 494,547 Claims priority, application France, Sept. 21, 1965, 32,083, Patent 1,423,911; Nov. 25, 1965, 996,238, Patent 88,772

8 Claims. (Cl. 313-109) ABSTRACT F THE DISCLOSURE An electric discharge lamp of the high pressure mercury vapour type, containing rare gas, mercury and halides of indium, thallium and gallium. The electrical loading of the lamp is comprised between and 20 watts per square centimeter of the internal wall of the discharge tube. Preferably, the halides are iodides and their respective proportions by weight are:

Percent Indium monoiodide 20-50 Thalium monoiodide 20-40 Gallium triiodide 10-50 3,379,916 Patented Apr. 23, 1968 to produce a light, of which the distribution is suitably balanced in all parts of the visible spectrum.

Another object of my invention is to provide an electric discharge lamp of the above stated type the discharge 5 atmosphere of which comprises a mixture of indium halide, thallium halide and gallium halide preferably in the dry vapor state in running conditions.

The radiation emitted by the mixture of these metal halides, preferably metal iodides, covers the whole of the lo visible spectrum. In addition, at the cold point temperature of a conventional high-pressure mercury lamp, which temperature is of the order of 600 C., the vapour tensions of the iodides indicated above are appreciable and in fact are approximately, in millimetres of mercury:

Mm. Indium iodide 200l Thallium iodide 40 Gallium triiodide 3000 A composition giving a white light with an acceptable colour emission and with a high luminous efficiency of the order of 80 lm./w., introduced into a conventional high pressure 400 Watt mercury vapour lamp with an external diameter of 17.5 mm. and an electrode spacing of 55 mm. is as follows:

Mg. Mercury 25 Indium monoiodide 5.0 Thallium monoiodide 3.5

Gallium triiodide 5.0 The internal volume of the tube being about l1 cm, these weights correspond to the following weights per cm.3 of the tube:

Mercury 2.30 Indium monoiodide 0.46 Thallium monoiodide 0.52 Gallium triiodide 0.46

in the state of saturated vapour at the temperature of the coldest inner point of the discharge tube. This is particularly the case with sodium iodide which has to be used in excess if its not to disappear rapidly due to absorption by the elements of the discharge tube. On the other hand, harmful eifects, such as the blackening of the wall, were observed in those cases where an excess of sodium iodide was used, this being in addition to the disappearing phenomenon; these effects may be due to a decomposition of the sodium iodide under the action of the high temperature of the electrodes, it being possible for the liberated sodium to attack the wall.

Furthermore, if there is used a mixture of mercury and halides, of which certain constituents are in the saturating vapour state, as is the case in practice with sodium iodide,

and the others are in the dry vapour state, as is the case with the mercury and may be so with the indium and thallium iodides, the proportions of these substances in the gas of the discharge atmosphere under normal running or operating conditions may vary appreciably because of the variation of the cold point temperature due to variations in external conditions such as those of the line voltage and of the ambient temperature. This temperature characteristic is found to vary from one lamp to another of the same manufacture, lbecause of small but inevitable deviations in their dimensions. It is also found to vary for the same lamp, depending on the supply voltage and the supply apparatus.

The object of our invention is to obviate these disadvantages by using a mixture of halides which does not comprise sodium iodide and of which the components have a sufficient vapour tension in order to be able to function in the dry vapour state; this mixture is chosen so as These quantities can be subject to variations, depending on the desired object. Nevertheless, since one of the essential contributions to the radiation which is produced is the blue radiation of indium with a Wavelength of 4511 A. and since this radiation is a resonance radiation, it is important that it is not self-absorbed to an appreciable degree, as would be the case if the quantity of indium iodide were too greatly increased.

Taking into account the ratios to be observed between the indium, thallium and gallium iodides in order to ob- 50 tain a light of sufliciently white appearance, it is necessary,

when maintaining the above quantity of mercury, to limit the total quantity of the iodides introduced in the form indicated above to not more than 6 mg. per cubic centimetre of internal volume of the discharge tube.

The spectral distribution of the radiation can be caused to vary, for example, in order to favour either the obtaining of blue light, or the obtaining of green light, or the obtaining of red and violet light, respectively by increasing the proportions of indium iodide, thallium iodide and gallium iodide.

Nevertheless, it has been found that, in order that the emitted light remain of fair quality, it is desirable to respect the following limits, in percentages by Weight with respect to the total quantity of iodides introduced:

portions obtained for the metals must be equivalent t0 those resulting from the above limits and preferably at least one of the metals is present, at least in appreciable proportion, in triiodide form.

In operation, the triiodides result in more iodine being liberated in the discharge, this facilitating the wall of the discharge tube being kept free from any harmful deposition by favouring the iodine cycle, which is Well known for avoiding the deposits of tungsten in iodine incandescent lamps.

The discharge vessel is advantageously equipped with tungsten electrodes comprising an addition of thorium in metallic form as an element which easily emits electrons. This thorium may in addition contribute to the light emission by production of thorium iodide from iodide in excess, coming from the triiodide.

The use of gallium iodide, emitting red light of Wavelengths 6414 and 6397 A., involves the production of violet light of wavelengths 4032 and 4172 A. These violet radiations, which are less efficient from the point of view of light production, can advantageously be employed for exciting a tluorescent material deposited in a bulb containing the mercury and iodides vapour tube. This fluorescent material, which must have good eiciency at the high temperature of the bulb, will for example be magnesium uorogermanate emitting red light or preferably strontium and optionally zinc orthophosphate activated with tin, an emitter of orange and yellow radiation and contributing to the balance of the light in the different parts of the spectrum.

FIGURES 1 and 2 show diagrammatically and by Way of example two lamps according to the invention.

In FIGURES 1 and 2, the reference 1 represents the discharge tube. This latter is formed by a tube ot fused transparent silica with an internal diameter of about 15 mm. and containing an electrode 2 or 12 at each of its ends. Each of these electrodes is for example formed of a tungsten rod around which is a coil of tungsten wire, a piece of thorium metal being gripped by the coil on the rod. An auxiliary electrode 3 is placed at one end near a main electrode in order to facilitate the igniting operation. A resistance 5 of about 20,000 ohms is connected between the auxiliary electrode and the opposite main electrode.

In FIGURE 1, the silica tube 1 is mounted axially in a cylindrical envelope 6 of hard glass in known manner by means of a metal support.

Fixed around the ends of the silica tube are heat-insulating elements 4, 14 which are formed by a metal strip of polished nickel insulated from the end of the lamp by a thermal insulator, such as for example silica wool. This permits the heat losses through the ends of the tube to be greatly reduced, especially when these latter comprise flat pinched portions with a large area. In this way, a suciently high temperature, of the order of 600 C., is maintained at the cold point of the tube, thus avoiding the possible condensation of the products being used and permits a more rapid warming-up.

The silica tube 1 contains a rare gas, such as argon, under a pressure of the order of 20 mm., or a mixture of rare gases, and a quantity of mercury of the order of 25 mg. in order to obtain an operating voltage of 135 volts with the power of 400 watts. The metal iodides which have been referred to above are added to the mercury and these are represented in the form of a patch 1I. Such lamps have a starting voltage of the order of 250 volts, which can be brought to below 200 volts by the use of heated electrodes, particularly for starting.

The silica tube 1 which has been illustrated, having a consumption of 400 watts and the dimensions as indicated, only contains dry vapours under running conditions, even if a vacuum has not been produced in the space between it and the envelope 6. This space can thus be filled with a neutral gas; nevertheless, the use of vacuum permits a more rapid warming-up.

In the form of lamp as shown in FIGURE 2, a bulb 8 of ovoidal form is used as the external envelope, on the internal surface of which is deposited a luminescent material 9, such as zinc and strontium orthophosphate activated with tin or magnesium fluorogermanate; the fluorescence of this material modifies the colour of the light emitted by the lamp. Moreover, it is possible for several fluorescent materials to be used simultaneously.

It may be advantageous to form the bulbs 6 and 8 of slightly yellow glass or to deposit inside these bulbs a layer which is formed wholly or in part by a yellow pigment; in this way, a light is obtained which has a more accentuated component in the long wave lengths.

The means indicated above can be applied with cornparable results in a very wide power range While varying or not the dimensions of the tube 1; however, it is necessary for the mercury and the iodides to be in the dry vapour state under working conditions.

The advantages of the lamps according to the invention are as follows:

By using the components of the discharge atmosphere in the dry vapour state, a constancy of the color of the emitted radiation is obtained, this colour not depending in practice either on manufacturing operations, or on the duration or on variations in the supply conditions; the production of permanent light-absorbent deposits is avoided; the use of compounds of metals of the same group of the Mendeleef classification, having very similar chemical properties, this simplifying the protection against the action of these metals; the use of compounds of metals which do not have any great chemical activity with respect to the elements of the discharge tube; by the use of one the halides in the form of triiodide, the action of the iodine is reinforced as regards the volatilisation of the metals which may come from the electrodes and be deposited on the walls; the obtaining of a substantially white light by the combination of the spectra of the different elements, with a high luminous efr'iciency.

The lamps according to the invention have the above advantages, as well as a high e'iciency, without it being necessary to dissipate therefrom a high power, relatively to their dimensions; there are thus avoided the disadvantages of a high temperature due to a high load: rapid devitrification of the silica forming the wall of the tube, rapid destruction of the tube, more rapid physical and chemical phenomena and probably opaque metals deposition on the wall of the tube may be with a surface attack of the silica.

The following table shows the range of electrical characteristics which have given good results for lamps of 400 watts7 showing various shapes.

Min. Mean N ax Current density in a cross section of the discharge (amo/am?) 0.7 1. 5 2. 5 Watts per om. of discharge 40 75 130 Watts per cm.2 of internal surface 10 14 20 Watts per ce. of internal volume of the tube 15 30 100 Potential gradient, 10 25 50 The mean characteristics correspond to a tube having approximately the following dimensions:

argon under a pressure of 20 mm. Hg at 15 C.

For lamps from w. to 2,000 w., the practical limits of the electric loading still are l0 to 20 w. per crn.2 of internal surface of the discharge tube.

The invention can be carried into effect in ways different from those described above.

For example, all or part oi thc mercury can be introduced in iodide form, possibly by reducing or by suppressing the use of triiodide or other trihalide.

It is also possible to use halides other than the iodides, and halides of metals other than those indicated above, provided that these halides are in the dry vapour state when the lamp has reached its normal running equilibrium.

What We claim is:

1. A high-pressure mercury vapour lamp comprising a discharge tube containing two electrodes and a discharge atmosphere, wherein said atmosphere comprises at least rare gas, mercury and a mixture of indium halide, thallium halide and gallium halide, the total quantity of the halides being not more than 6 mg. per cc. of volume of the discharge space, the halides being in the dry vapour state under running conditions and the electrical loading of the lamp being comprised between 10 and 20 watts per square centimeter of the internal wall of the tube.

2. A high-pressure mercury vapour lamp comprising a discharge tube containing two electrodes and a discharge atmosphere, wherein said atmosphere comprises at least rare gas, mercury and a mixture of indium halide, thallium halide and gallium halide, in which the respective proportions of indium, thallium and galliurn metals correspond to the following proportions by weight of their iodides:

Percent indium monoiodide 20-50 Thallium monoiodide 20-40 Gallium triiodide 10-50 the halides being in the dry vapour state under running conditions and the electrical loading of the lamp being comprised between l0 and 20 watts per square centimeter of the internal wall of the tube.

3. A high-pressure mercury vapour lamp comprising a discharge tube containing two electrodes and a discharge atmosphere, wherein said atmosphere comprises at least rare gas, mercury and a mixture of indium halide, thallium halide and gallium halide, in which at least one of the metals indium, thallium, gallium is combined with two halogens, the halides being in the dry vapour state under running conditions and the electrical loading oi the lamp being comprised between 10 and 20 watts per square centimeter of the internal Wall of the tube.

4. A lamp as claimed in claim 1 in which said halides are iodides.

5. A lamp as claimed in claim 1 in which one at least of said halides is a triiodide.

6. A lamp as claimed in claim 1 in which an envelope coated with luminescent substances, composed of at least one phosphor selected from the group consisting of strontiumand orthophosphate treated with tin, strontium and zinc orthophosphate activated with tin and magnesium tluorogermanate, is disposed around the discharge space.

7. A lamp as claimed in claim 1 in which an envelope absorbing at least partially the visible radiations of short wavelength is disposed peripherally around the discharge space yof said vapour lamp.

8. A lamp as claimed in claim 1 in which at least one of said electrodes includes thorium in metallic form.

References Cited UNITED STATES PATENTS 3,234,421 2/1966 Reiling 313-299 X 3,259,777 7/1966 Fridrich 313-225 X 3,274,415 9/1966 Thomas 313-108 X JAMES W. LAWRENCE, Primary Examiner. S. A. SCHNEEBERGER, Assistant Examiner. 

